1. Field of the Invention
The present invention relates to a holographic recording medium and more particularly, to a medium in which holographic recording/reproducing can be performed after a recording position or a reproducing position is detected in the medium.
2. Description of the Related Art
According to a conventional magneto-optical recording medium (such as MO), while address information previously recorded on the medium is detected, a seek operation is performed in which an optical component and the like is moved by a distance corresponding to a difference between a detected present address and a target address in which recording (or reproducing) is to be performed, and after the present address coincides with the target address, information is recorded/reproduced.
FIG. 21 is a schematic explanatory view showing a recording region of the conventional magneto-optical recording medium.
Referring to FIG. 21, an address region and a data region are alternately arranged on one track and, for example, just after a certain address region, a data region corresponding to that address region is arranged.
In addition, in one address region, a row of pits is formed to specify an address specific to the address region.
The row of pits is formed in the address region shown in FIG. 21 and a target address is searched by reading the pit row and data is recorded in the data region corresponding to the target address.
If the recording is performed before the target address and the present address coincide with each other, existing data could be destroyed or data which is different from the target data is read out due to a defect of reproduction. As a result, normal recording/reproducing cannot be performed. Thus, it is very important to confirm that the present address and the target address coincide with each other. Such confirmation of the address coincidence is also important in a holographic recording medium in which two-dimensional page data is multiplex-recorded.
Japanese Unexamined Patent Publication No. 2005-31395 proposes an address information adding method in which address information is arranged together with data in a two-dimensional information page to facilitate an addressing operation, and a position error between the address information and holographic data can be detected. Here, there is described a holographic recording medium in which a position of an address information region is differentiated every page, and an address is detected by a sum of detected light amounts, and after the multiplex-recorded two-dimensional page information is reproduced, position displacement can be detected.
However, according to the holographic recording, since plural pieces of information (two-dimensional page data) are multiplex-recorded in the same physical region, its recording density is considerably high as compared with the conventional magneto-optical medium (such as MO). Therefore, if an address is allocated to one recording unit like the conventional MO, since a ratio occupied by recording region to be used for recording the address information is increased, it is actually difficult to allocate the address like the conventional MO.
Thus, according to the conventional holographic recording, it is difficult to confirm that the target address coincides with the present address every recording unit before the data is recorded or reproduced like an address detection process of the conventional MO.
In addition, according to Japanese Unexamined Patent Publication No. 2005-31395, the position displacement of the recording or reproducing position can be detected after the two-dimensional page information containing the address information is reproduced. However, since the recording capacity of the page information which is one unit for the recording/reproducing is very large such as hundreds of megabytes, it takes a lot of time to reproduce the page information itself.
That is, since it is found that the address information is different from the target address after the page data containing the address information is reproduced, which takes a lot of time, a waste time is consumed for the reproducing, so that it takes a lot of time to perform the reproducing process substantially.
In addition, according to the holographic recording in which it takes time to reproducing the data, it is desirable that the address information to be reproduced is detected and then it can be detected that the address information is displaced before the reproducing process of the two-dimensional page data in order to improve time efficiency in reproducing the page data.